NUNATAK AND CASCADING GLACIERS 141 Hidden Glaciers. In a tidal ice tongue like the Nunatak Glacier the future behavior is to be watched with the utmost interest. If the advance is attributable to .the avalanche supply during the 1899 earthquakes, as we believe, this glacier has taken between ten and eleven years to respond to the accession in the snowfields and upper glacial tributaries. If the slight advance in 1910 was due to the thrust of a small tributary there may yet come a greater advance due to the activity of larger tributaries. If no advance comes in the next few years we shall perhaps be warranted in ascribing the lack of great advances of the Nunatak, Hubbard, and Turner Glaciers to their tidal condition. The following tabular statement shows the known history of the tidal arm of Nunatak Glacier up to 1913: Year Nature of Change Observer Before 1891 Probably retreat Russell 1891-1895 Retreat Boundary Survey 1896-1899 Retreat about 4600 feet Gilbert 1899-1905 Retreat about 5300 feet Tarr and Martin 1905-1906 Retreat Tarr 1905-1909 Retreat about 3300 feet Tarr and Martin 1909-1910 Advance 700-1000 feet Martin 1910-1911 Advance* slight Boundary Survey 1911-1912 Retreat about £ mile Boundary Survey 1912-1918 Retreat, slight Martin CASCADING GLACIEB General Description. Gilbert: who photographed and named the Cascading Glacier in 1899, when Gannett2 showed it upon the map of Nunatak Fiord, speaks of it as oo-•cupying a high valley nearly at right angles to the Nunatak trough. "It was seen only as a series of ice cascades, pouring from ledge to ledge for a thousand feet down the steep 'wall of the trough." Its valley lies entirely above snow line and heads a few miles to the 'south in the mountains that lie between Hidden Glacier and Nunatak Fiord. The characteristics of the glacier in this valley are unknown excepting at the very edge, but it is probably not materially unlike scores of other short, high, mountain valley glaciers. The most noteworthy feature of the Cascading Glacier is that on reaching the end of its high valley, at an elevation of 1500 feet or more above the fiord, its slope abruptly changes and it descends the steep south wall of Nunatak Fiord in a series of steps, with greatly-broken surface (PI. LX, B), like a frozen waterfall on the mountain side, which, from its resemblance to a cascade, led Dr. Gilbert to give this glacier its name. The slope over which this glacier descends is so steep that it is doubtful if the glacier could cling to it were it not for the fact that there are two pronounced rock terraces and several smaller ones (PL LXX3I, A), caused by the fluting of the valley side by earlier glacial erosion, when the former expanded Nunatak Glacier rose up over the valley side 11 Gilbert, G. K, Harriman Akska Expedition,. Vol. 3, 1904, p. 60. •Gannett, Henry, Same, PL HI opposite p. 58.